Forensic teams sealed off the home and began investigating. More than two months after she was found, police say they suspect foul play.
"Investigators believe Sarah died between April 20 to 24. Forensic evidence has indicated that a violent assault took place within the premises," Victoria Police said in a statement today.
"They also believe that her body was deliberately concealed at the address and conscious steps were taken to imply she was still alive after her death."
Police arrested three men and two women shortly after the discovery of Gatt's body. They say all were questioned by police but none were charged. All five were released pending further inquiries.
Officer in charge of the Homicide Squad, Detective Inspector Tim Day, said police were keen to speak to anyone who believed Gatt was alive after April last year.
"It's disturbing and concerning to investigators that it appears someone has deliberately attempted to make it look as though Sarah was still alive," he said.
"There are people out there who know what happened to Sarah and we are urging them to come forward and speak to police.
"We are particularly keen to speak to anyone who saw any person coming or going from her Lambeth St unit after April 20 last year."
He said that could include "a range of people including neighbours, friends, passers-by or any local businesses she had contact with."
Gatt had four children, however none of them were living with her at the property at the time of her death.
